In a T3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) communications system, time-and-frequency resources in each downlink subframe are divided into two regions: a downlink control channel region and a downlink data channel region. The downlink control channel region occupies the first N orthogonal frequency division multiplexing (OFDM) symbols, where N is less than or equal to 3, and the downlink data channel region occupies the remaining OFDM symbols. A physical downlink control channel (PDCCH) is used to transmit scheduling indication signaling for user uplink or downlink data transmission, for example, information related to data channel resource allocation, a modulation and coding scheme, multi-antenna transmission, a hybrid automatic repeat request (HARQ) process, and so on. The PDCCHs of multiple users share the time-and-frequency resources of the downlink control channel region. A physical downlink shared channel (PDSCH) is used to transmit user downlink data, and occupies the time-and-frequency resources of the downlink data channel region.
Because both uplink and downlink data scheduling of each user needs to be indicated by the PDCCH, the capacity of the downlink control channel region is a key factor affecting the number of users that can be scheduled in a cell simultaneously. A coordinated multi-point (CoMP) scheduling mechanism and a more flexible multi-user multi-input multi-output (MU-MIMO) scheduling mechanism are introduced, so as to provide higher spectrum efficiency and cell edge user performance, and significantly increase the number of users that can be simultaneously served by the cell. As a result, the downlink control channel region of three OFDM symbols in the LTE system cannot meet requirements, and therefore, an extended PDCCH (E-PDCCH) emerges for transmitting scheduling indication signaling for uplink or downlink data transmission of more users. The E-PDCCH occupies some time-and-frequency resources of the downlink data channel region, and shares the time-and-frequency resources of the downlink data channel region with the PDSCH by using frequency division multiplexing (FDM), or by using time division multiplexing (TDM) together with frequency division multiplexing.
The E-PDCCH performs demodulation based on a demodulation reference signal (DMRS), and the DMRS is specific to a user equipment (UE). An initial value of the DMRS is determined according to both a cell identifier (Cell ID) and a scrambling identifier (SCID). For the E-PDCCH, the SCID and the E-PDCCH are notified together to a UE. As a result, the UE cannot know the SCID beforehand, and cannot know the DMRS required for demodulating the E-PDCCH, and therefore cannot demodulate the E-PDCCH.